Earnings Per Share - Schedule of Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic earnings per share
Net income from continuing operations	$ 73.0	$ 64.3	$ 179.0	$ 153.3
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.5)
Income before discontinued operations available to common shareholders - Basic	72.8	64.1	178.4	152.8
Income (Loss) from discontinued operations, net	(61.9)	(1.5)	(59.4)	2.4
Amount allocated to nonvested participating shareholders	0	0	0	0
Income (Loss) from discontinued operations available to common shareholders - Basic	(61.9)	(1.5)	(59.4)	2.4
Net income	11.1	62.8	119.6	155.7
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.5)
Net income available to common shareholders - Basic	10.9	62.6	119.0	155.2
Average common shares outstanding - Basic	227.8	215.2	220.3	214.9
Earnings per share from continuing operations - Basic	$ 0.32	$ 0.30	$ 0.81	$ 0.71
Earnings per share from discontinued operations - Basic	$ (0.28)	$ (0.01)	$ (0.27)	$ 0.01
Earnings per share - Basic	$ 0.04	$ 0.29	$ 0.54	$ 0.72
Diluted earnings per share
Net income from continuing operations	73.0	64.3	179.0	153.3
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.5)
Income before discontinued operations available to common shareholders - Diluted	72.8	64.1	178.4	152.8
Income (Loss) from discontinued operations, net	(61.9)	(1.5)	(59.4)	2.4
Amount allocated to nonvested participating shareholders	0	0	0	0
Income (Loss) from discontinued operations available to common shareholders - Diluted	(61.9)	(1.5)	(59.4)	2.4
Net income	11.1	62.8	119.6	155.7
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.6)	(0.5)
Net income available to common shareholders - Diluted	$ 10.9	$ 62.6	$ 119.0	$ 155.2
Average common shares outstanding - Basic	227.8	215.2	220.3	214.9
Assumed conversion of stock options, unvested restricted stock and contingent performance shares, net	0.5	0.4	0.5	0.5
Average common shares outstanding - Diluted	228.3	215.6	220.8	215.4
Earnings per share from continuing operations - Diluted	$ 0.32	$ 0.30	$ 0.81	$ 0.71
Earnings per share from discontinued operations - Diluted	$ (0.28)	$ (0.01)	$ (0.27)	$ 0.01
Earnings per share - Diluted	$ 0.04	$ 0.29	$ 0.54	$ 0.72
Anti-dilutive shares	0	0	0	0